How do I tell red oak from white oak?

Q:

I’m trying to match some wood in an old house, and although I know it’s oak, I’m not sure how to tell red oak from white oak. Is there a telltale sign?

J. Burke, None

A:

Despite their similar names, these two woods are very different. White oak is slightly harder than red oak and is far more durable in exterior conditions, which is why it’s popular in boatbuilding. There are a few ways to help distinguish the two woods, but some clues are more reliable than others. Once you have some experience working with both, you’ll likely be able to distinguish them by something as simple as their smells. White oak is said to have a distinctly sweet smell. For beginners, here are some other helpful tricks.

A good place to start. If the wood is unfinished, color can be a strong indicator. Sometimes the difference in color is subtle, and sometimes it’s obvious. Red oak tends to be reddish-pink, and white oak is light brown. The age and condition of the wood can make differentiating species more difficult, especially because shades of red often fade to brown, which makes this test among the least reliable.

Another challenge is that there is only one true species of red oak (Quercas rubra) and of white oak (Quercas alba), but there are 20 other varieties commonly grouped under the “red oak” or “white oak” heading based on their characteristics, so the possible color variations can be significant.

A bit more reliable. If you’re able to make a fresh cut into the wood in question, there are a couple of fairly reliable hints in the grain structure. First, look at the rays. When red oak is flat-sawn, which is the most common cut of lumber, the rays on the surface are rarely more than about 1/2 in. long. By contrast, the rays in white oak are typically at least 1 in. long.

Second, check the end grain. A visual inspection of end grain reveals more open cells in red oak than in white oak. The reason for this is the continuous nature of red-oak cells vs. the segmentation of white-oak cells. Here, a wicking test is revealing. If you place red oak with the end grain down in denatured alcohol, the alcohol wicks through quickly, while doing the same thing with white oak results either in no signs of wicking or only slight evidence at radial checks. In fact, the cell structure of red oak is so consistent that you can typically submerge one end of a short piece of red oak in water and blow bubbles through it.

Nearly foolproof. If you have to know for sure, you can do a color-changing experiment. Apply a test spot of a diluted solution of sodium nitrite to the surfaces of the two woods. The solution may darken red oak slightly, but it will turn white oak a deep indigo color, or even black.

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